1. Field of the Invention
The present invention relates to a microwave solid-state oscillator constructed to control an oscillation frequency by means of a dielectric resonator and particularly to a microwave solid-state oscillator having its own frequency and an output regulation device.
2. Description of the Prior Art
A high-Q dielectric resonator having an excellent temperature stability is commonly used as a microwave oscillator demanding high stability, such as a local oscillator for microwave radio equipment. Usually, the microwave solid-state oscillator is constructed with a semiconductor oscillation device, such as a Gunn diode or an FET, mounted on a microstrip line formed on an insulated substrate made of alumina, and the oscillation device is made to be electromagnetically coupled to a dielectric resonator.
In this instance, the semiconductor oscillation device is often used as a state of a flip-chip of semiconductor in order to miniaturize an oscillator and to eliminate stray reactance in the device. With this condition, the dielectric resonator or the whole construction of the oscillator must be hermetically sealed to protect the dielectric resonator from moisture.
In the oscillator having such a dielectric resonator, the oscillation frequency generated therein fluctuates due to lack of uniformity of characteristics of the materials of the dielectric resonator or the semiconductor device and, further, due to the relationship of the dielectric resonator to the microstrip line or a sealed casing wall. Accordingly, the predetermined oscillation frequency or output is not regularly obtained. Moreover, in a local oscillator directly connected to a mixing circuit, it is very hard to regulate a load impedance of the local oscillator at a certain value. Thus, re-regulation of the oscillation frequency has been required.
Consequently, the microwave oscillator having a dielectric resonator demands equipment to regulate the oscillation frequency even after the dielectric resonator or the whole construction of the oscillator is hermetically sealed.
Conventionally, the equipment having a construction shown in FIG. 1 is used as the regulation equipment for oscillation frequency.
Namely, as shown in FIG. 1, microstrip line 1A upon which is mounted a semiconductor device (not shown) is formed by a microwave integrated circuit (hereinafter referred as MIC), which is disposed on substrate 1 made of an alumina. An oscillator is constructed by mounting dielectric resonator 2 on supporting base 3 made of dielectric materials having a small dielectric constant and electromagnetically connecting the dielectric resonator to the MIC.
Oscillation output terminal 4 is hermetically attached to lower case 5 by means of solder. Upper case 6 provides screw box 6A to accept adjustment screw 7 and provides cylindrical projection 6B. Hermetical sealing between adjusting screw 7 and upper case 6 is obtained with the aid of O-ring 8 mounted inside cylindrical projection 6B. Further, O-ring 9 provides hermetical sealing between upper case 6 and lower case 5.
With this construction, turning of adjusting screw 7 varies the distance 1 between the top surface of the dielectric resonator and the tip of the adjusting screw 7. By this variance, oscillation frequency can be varied while retaining the oscillator under the hermetically sealed condition.
Another prior art construction is illustrated in FIG. 2. Namely, microstrip line 11A mounting a semiconductor device is formed by the MIC, which is disposed on a substrate 11 made of an alumina. An oscillator is constructed by mounting dielectric resonator 12 on supporting base 13 made of dielectric materials having a small dielectric constant and electromagnetically connecting the dielectric resonator to the MIC.
Oscillation output terminal 14 is hermetically attached to lower case 15 by means of a solder.
Supporting base 13 which is cylindrically formed is closed at the side toward dielectric resonator 12 and is directly mounted to lower case 15 through bore 11B formed in substrate 11 by means of an adhesive agent. Adjusting screw 17 is mounted inside supporting base 13 through screw box 15A. Upper case 16 is flat and the junction between the upper case and lower case 15 is hermetically sealed with the aid of O-ring 18.
With this construction, turning of adjusting screw 17 varies the distance 1 between the bottom surface of dielectric resonator 12 and the tip of adjusting screw 17. By this operation, oscillation frequency can be varied while retaining the oscillator under the hermetically sealed condition.
Since, as stated in the above-mentioned two prior art constructions, the conventional method for regulating an oscillation frequency is carried out by adjusting the gap between the tip of the adjusting screw and the dielectric resonator and requires among other things, a screw and an O-ring, these conventional devices require minute mechanical work, are large in size and are very expensive. Moreover, since hermetical sealing is retained by means of an O-ring or an adhesive agent, the degree of airtightness has been low (being about 10.sup.-5 to 10.sup.-6 atm cc/s) and moisture-proofing has been hard to obtain.